Extracellular vesicles (EVs) are considered as valuable biomarkers to discriminate healthy from diseased cells such as cancer. Passing cytosolic and plasma membranes before their release, EVs inherit the biochemical properties of the cell. Researchers from ETH Zurich determine protein profiles of single EVs to understand how much they represent their cell of origin. They use a microfluidic platform which allows to immobilize EVs from completely isolated single cells, reducing heterogeneity of EVs as strongly seen in cell populations. After immunostaining, the researchers employ four-color total internal reflection fluorescence microscopy to enumerate EVs and determine their biochemical fingerprint encoded in membranous or cytosolic proteins. Analyzing single cells derived from pleural effusions of two different human adenocarcinoma as well as from human embryonic kidney (SkBr3, MCF-7 and HEK293, respectively), they observed that a single cell secretes enough EVs to extract the respective tissue fingerprint. They show that overexpressed integral plasma membrane proteins are also found in EV membranes, which together with populations of colocalized proteins, provide a cell-specific, characteristic pattern. This method highlights the potential of EVs as a diagnostic marker and can be directly employed for fundamental studies of EV biogenesis.
Workflow for detecting and identifying EV populations form single cells
(A) Using fluorescently conjugated mAbs and four-color TIRFM, we image immobilized EVs (B) in the direct neighborhood of the cells, which are prevented from cross-contamination with EVs from other cells. (C) Multicolor TIRFM images of secreted and immobilized EVs. (D) Customized Matlab imaging processing allows for quantifying and identifying EVs per image. Note that the histograms display raw data (detected signals per image).